Tar and Gravel Roof - Patch large opening

Hello,

I have a low pitched (2/12) tar and gravel roof. It was built up using gravel on top of tar mats, on top of 2" fiberboard for insulation on top of 4x6 roof rafters. A chimney was removed which created a 30" x 30" opening spanning from rafter to rafter. The opening was filled with layers of plywood (for structural support) and the same type of fiberboard that is used everywhere else on the roof. The uncovered area is now filled up to just below the tar mats.

How would I now patch this rather large opening? Should tar mats and tar be used or can it be patched with a different kind of roof covering where the seams would be sealed with some kind of roofing caulk?

Thanks guys!

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Tar and Gravel Roof - Patch large opening

Find a company that has the tools and know-how to do it correctly. You have a built up roofing system and it should be repaired in the same manner. Built up with layers of seaming membrane and hot mopped product.

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Tar and Gravel Roof - Patch large opening

I went out and got a few quotes. They are really high because there are almost no contractors around in this area that still do work on tar and gravel roofs. I called many (if not all) roofers in the area and that is what I was told.

Tar and Gravel Roof - Patch large opening

Tar and Gravel Roof - Patch large opening

You don't have to have a kettle and mops felts down to patch this small area. It wouldn't be wrong to do it that way - but I can imagine you would have a hard time getting someone to fire up a patch kettle for something this small.

First - "tar" vs "asphalt". - These are not interchangeable words and are two different roofs and materials. The methods of repair are also different as you cannot take asphalt based products to patch a tar roof. Since you have a 2/12 roof you very likely have an asphalt roof and will need asphalt materials to repair. Tar is typically used on dead flat roof or very low pitched roofs as it will get soft enough to run right off the side of the building. Dropping a piece of asphalt or tar from the roof in a small container of mineral spirits will tell you for sure what you have. Asphalt will quickly start dissolving and turn the liquid black or dark brown. The tar may dissolve more slowly turning the liquid a yellowish green.

The difficult part of the repair is to strip the gravel off the felts back around the perimeter of the hole 8 to 12 inches. You will have to use a flat bar for this and very carefully scrap the gravel off the felt without damaging the felts. Best done in the early morning when the roof is cool. This will give you a edge on the old roof to tie the new patch material into. (You don't want to apply anything over the rock, the rock must be cleaned back)

Now you can use cold process type of materials to patch the hole. Nail or adhere a base sheet over the new wood and try to tuck it under the old felts. Then apply a cold process adhesive with a smooth modified to patch over the hole and tie into old roof you cleaned. (I can go in more depth here if needed, but roofing supplier can help get you the proper materials)

I would still encourage you to seek out an old roofer to do this. Call the roof supply houses around to get a name of one. By time you buy the materials and take the risk of tearing up your roof you will likely be better off getting the roofer to do it. You will have to buy full roll and bucket to do this and have a bunch leftover to only fix a small hole. This is a simple repair that can be done in a couple of hours from a roofer that may have enough material laying around his shop.

Also - a roofer can torch the modified patch down in lieu of using the cold process. Just need to be be very sure the roofer knows what he is doing since you have the 2" of fiberboard. Fiberboard can smolder for days before you actually see the fire and smoke billowing from your roof.

Tar and Gravel Roof - Patch large opening

Quote:

Originally Posted by Jaxx

I went out and got a few quotes. They are really high because there are almost no contractors around in this area that still do work on tar and gravel roofs. I called many (if not all) roofers in the area and that is what I was told.

Any alternative routes for me?

This is an insightful thread. I was just wondering, how high is the cost of this repair by contractors vs a complete reroof to a modern roofing system (e.g. shingles?). Did you mean high cost in terms of a repair or high cost in relation to a reroof/new roof job? Just curious to know.